This invention relates to an advance mechanism for a mine roof support assembly.
A known type of mine roof support assembly is constituted by a plurality of roof support units positioned side-by-side along, for example, a longwall face. Each of the units has a roof shield supported on a floor sill by means of hydraulic props. In order to advance the assembly to follow the advance of the longwall face, the roof support units are advanced, individually or in groups, by means of advance mechanisms. During the advance of any given unit, its hydraulic props are relaxed so that its roof shield is not under load.
A known type of advance mechanism for such an assembly comprises a pair of resilient guide rods and a pair of hydraulic advance rams. Such advance mechanisms are positioned between the floor sills of each pair of adjacent roof support units. The front ends of the guide rods of such an advance mechanism are attached to a head-piece which is connected, for example, to a longwall conveyor. The rear ends of the guide rods are unconnected, and are slidably guided in rod guides provided on the adjacent floor sills. The piston rods of the rams of each advance mechanism are attached to the front regions of the associated floor sills, and their cylinders are attached to the rear ends of the guide rods. Thus, the forces which advance the roof support units are transmitted through the full length of the guide rods. The rams of this type of mechanism are known as "braced-in" rams. (See DE-OS No. 27 58 663 and DE-OS No. 29 40 401).
The aim of the invention is to provide an advance mechanism of this type, which mechanism is of simple and space-saving construction style, and in particular has a low overall width, so that it is possible to dispense with the braced-in rams in favour of direct-acting rams. The advance mechanism should be such that extensive adjustability of the floor sills of the roof support units is possible, so that the mechanism can be used even with the known systems which are used to control the cutting horizon of a winning machine such as a coal plough.